1. Field of the Invention
The present invention relates to the fixing of the rotor blades to the drum of a turbomachine rotor.
2. Summary of the Prior Art
Several means are currently used for effecting the fixing and radial retention of the movable blades mounted on the wheels or rotors of modern turbomachines operating at high rotational speeds. Usually the blades, which are formed with a vane portion having an aerodynamic shape which ensures the desired performance of the compression or turbine stage for which the blade is designed, are provided with a base including a root which may be surmounted by a platform defining the inner wall of the main gas flow path. This root, which may be of hammer or fir-tree shape, is located in a cooperating axial groove provided in the rim of a wheel disc or in the outer periphery of a rotor drum. In some cases, the assembly may similarly be made in a peripheral or circumferential direction. In all cases, additional means are normally used to ensure locking of the blades in the radial, axial and peripheral directions.
These well known solutions are still widely used, particularly in aeronautical applications both in the military field and in the civil field, but are not entirely satisfactory in aircraft engines of new design, particularly those which incorporate an additional power turbine of slow rotational speed, intended to drive either a fan or a propeller, and including in particular two contra-rotating stages. As a particular consequence of the reduction of rotational speeds and therefore also of the level of stress to which the rotary parts are subjected, a lightening of the previously used technology is found to be practical. This lightness objective is accompanied by a search for simplification in order, particularly, to make assembly easier. Also, taking into account the new condition of use, the parts should exhibit good behavioural qualities at low rotational speeds of the rotor.
Some elements of a solution may be found in older arrangements which have not reached the degree of complexity and sophistication of more recent, better known solutions, and which are inadequate in themselves.
For example, U.S. Pat. No. 2,654,565 describes the mounting of blades in which the base includes shoulders forming hooks cooperating with slits provided on the rims of assembled discs to form a rotor. U.S. Pat. No. 3,063,674 illustrates the use of rivets for securing rotor blades.